Optoelectronic devices such as light emitting diodes (LEDs) contain areas made of semiconducting substances which emit light when an electrical current is applied. Current LEDs are based on compound semiconductors, especially so called III-V compound semiconductors such as Ga—N, Ga—P and Ga—As or multilayer assemblies such as Ga—N/In—Ga—N which are deposited onto substrate materials such as sapphire wafers and silicon wafers.
Said compound semiconductors need to be electrically connected to an electrical power source by electrodes. Due to undesired diffusion processes between electrodes and the compound semiconductor layer(s), conventional electrode materials such as aluminium or copper can not be used in LEDs. Instead, electrodes made of noble metals such as platinum or gold are used as electrode materials.
The electrodes are connected to the power source by soldering or bonding a conductor such as a copper wire onto the electrodes. Hence, a solderable and/or wire bondable surface needs to be attached onto the noble metal electrodes in order to obtain a sufficient electrical contact and mechanical reliability between the conductor and the electrode. Furthermore, the joints formed between the electrodes and the conductor need to be reliable.